Annealing furnace



Patented Feb. 12, i952 LQANEALING FURNAC s f i "Carl, Vifageger, Fairview Village, Ohio, assignor toJ ones v& jLaughlin Steel,` Corporation, Pittsi han, 11,

' applicati@ Jaim: s,

This invention relates to annealing furnaces, and in particular to Vvcover-typeanneali ng furnaces used for heat. treatingfthin,gaugeferrous material in the form of coilsor stacked sheets. It is an object ofmyinventionfto, provide' a furnace requiring less time thanl heretofore'for A, a corporation of nPennsylvania 1949,*seria1No. 102,376 y claims; (omas-42) heating strip or sheet. `It '1s-another object to inf1 crease the uniformity of temperature Which be obtainedinsuchafurnace. I

Cover-type annealing furnaces are widely used in the processing of ferrous sheet and strip@ Such furnaces, as conventionally l constructed, y'comprise a base and a removablecover.l..3The cover consists of a top and fouroside's yz'idaptedto fit over the base and enclose thecharge to be'heated. The means for supplying heat tof'th'e charge are may incorporated in the coverfandmay .be heating around the base and may be ls'ealedwith sand or similar material. Thiscovfer fis'liftedk on and 01T the base byv a crane,'the connections to elec"- trcal circuits, gas and airlines-and flues being arranged for convenient connection anddiscongnection. ff"

The conventional furnace 'base A usually consists of a steel shell in the'fo'rm ofa "shallow tray having a solidrefractry lining surmounted by brick checkerwork or stools of steel Vconstrue-,f tion supportingA` a floor platanponjwhich'the charge rests. It is customary` in steel millsto provide more bases thanV covers', .asv'covers are not needed while material is beingloaded @onto a base or removed therefrom after treat-mentor cooling during the last portion of the annealing cycle. ,f

One of the principal objects in thefdesignnbf heat-treating furnaces of most ftypes'.' is .the maintenance of a uniform temperaturethrough"-v out the charge being treated. In cover-typefur naces for treating strip or sheetthle'larrangement of the heating meanaaswelLasbther fac# tors affecting heat distribution, 'haswbeeithe sub'- ject of considerable investigation, as the conditions in furnaces of this type are inherently unfavorable tov uniform heating.' The charge is present either as coils,;usually tightly Wrapped, or as stacks of individual sheets, presenting solid masses of metal of largethermal inertia. Furthermore, these are generally enclosed in sealed boxes to prevent oxidation. lThe vheating"oftli'e charge thus proceeds very slowly, not infrequently extendingv over periods exceeding twentyffour hours. In operation the r'at'eofjheat 'ut-in such by the rate of heat absorption in the zone of the furnace leastfavorably heated. If, to accelerate heating in this zone, the heat input to the furnace is stepped up, overheating may occur in regions of Amore rapid heat absorption.

I have discovered that one factor limiting the rateof heating charges in cover-type' furnaces is'the considerable' absorption'of heat from the charge bythe furnace floor plate, Vstools and refractlorie's in the base. Thev heating means in the furnace Walls are designed and positioned to transfer heat to the charge but are not well ataptedjtgheat the base, which, furthermore, is shielded from the heating means by the material charged thereon.V Consequently, although heat is transferred into the charge through its faces adjacent the heating means, I have found that a considerable quantity is transferred by conductionout of the charge, into the floor plate and other base furniture. This continues until the base temperature reaches the temperature of the charge, that is to say, throughout the whole of the heating period. This heat transfer from charge to base prolongs the heating period and aggravates temperature differences normally existingbetweenthe top and bottom of the charge.

I have further discovered that `these conditions can be alleviated by the provision of heating means suitably `disposed in the furnace base. In a preferred form of my invention, I provide a furnace of the cover type, having heating means in the side walls of the furnace and additional heating means jcentrally located in its base.y The heating tubes or other lmeans in the cover or superstructure furnish lthe great bulk of the heat requiredior the heat treatment of the charge. The heating tubes in the furnace base furnish a relatively small proportion ofthe total heat required but supply this heat under the floor plate in the central zone of the base, a region relatively poorly heatedA in conventional cover-type furnaces. Thisrelatively small amount of heat supplied through the furnace base in accordance with my invention makes possible a'great improvement inthe heating-characteristics of the furnacev with a consequent increase vin furnace productivity. The details of my invention will be explained in the course ofthe following description of the preferred lembodiment abovementioned, which is illustrated in the accompanying drawings.

the drawings Figure l is a plan view of the base of afurnace constructed according to my invention as .itwould appear with the floor plate removed. VOnly'thel left-hand end of the base is shown, it being understood that the right-hand end is a duplicate thereof.

Figure 2 is an elevation, partly in section, of a furnace constructed according to my invention,

taken on the plane II-II of Figurel.

a furnace islimited among? other''v-factors In these figures the furnace base comprises a shallowrectangular metal shell I, supported on I-be'ams" 2 or Aother suitable supports above the shop cor 3. This-shell I is illled with a layer 4 of refractory material, which may ordinary brick, or tile standing on end and lled with sand. Above this is a layer 5 of insulating brick. Upon this brick are spaced stools 6 which may be o'f welded steel construction. These stool's'are'uniformly located over the base and carry Atheuiloor plate l, which is a heavy steelpfatefpnwhieh the charge to be treated is placed. Achannel is provided around the outer edge of lthe base, which cooperates with means carried bythecover to seal off the furnace interior from -the --atmosphere.

I provide in each end'of the furnace base a U -shap'ed heating tube'havingparallel legs 9 tand across leg I0. The ends of this *tube are' brought out through sealing b'oxe'sfl'l attache'dfto theend of the base shell Vand'lled'with Sandor other suitable material. The'out'erend'poitions of fthe parallel legs 9 of 'the"heating"t'ube lie within the refractory layer '4 "in "channelsi'provided therein. The parallel legsV 9 are bent'oreffsetinthe*Vertical plane as 'shown infFigureZ'so that their inner end portions and thefcrossufl'egf li'e above"the insulating bricklayer "5." but' bfelo'i'vl'the floor' plate 1. A 4gas burner |`2 is Vll'ncfatd:in `the`op'en"'n'd of 'one of the parallel Ie'g's"9 fflthe heating tube and inoperation theopen'encrf thedtnerparallel leg 9 is connectedzt'o 'aua not shown. 'The gas burner `I 2 is prvided'with gas "and air con- "nec'tio'ns,` not shown.

The 'disposition Affthe heating tubes in the bas'eis evident rom 'F-igure '1. Th'e 'furnace ill and do notfurnish any considerable amount of heat to other regions ofthe furnace. This'function is assigned Vto the heating means infthe furnace cover, which will now descri'lbe. f

The cover comprises a metalrshell I3`-having a top and. four sides vlined with refractoriesV-I. A sealing `flange f5 fits into the channel-8 yofthe base. Heating tubes 1 6 areprov-ided in sidewalls of the cover for supplying=heat to the -furnace charge. These tubes maybe equippedwitmgas l that I have invented a furnace providing greater Vniformityof temperature throughout the charge larid'rhoerapid heating, thus making possible increased .production over that obtained from conventional :furnaces lthoug'hI havedescribed and illustrated the present preferred embodiment of my invention, it will 'be Ilhdr'stofd that the invention is not limitedthereto but may be otherwise embodied or practiced Within the scope of my claims.

v"1. In a heating'furnace'havinga rectangular "base land cover, the coverbeing 44provided with means for yintroducing 'hea't 'into the 'furnace 'hargegand'lthe basebei'ng; provided with a -plurality 'of 'supports'canyinga oor plate'on 'which the furnacejc'harge rests, the improvement consistingin' th'at'the''said4 supports are free standing supports spaced jto'p'e'rmit'th'e free circulation of the furnace atmosphere 'above 'and belowthe floor plate, and U =shaped7heating tubes disposed i'nthe center'po'rtion 'on'lybf the base below "the floor plate :andbetwe'e'n'the supports, thetub'es being 'Tpositoned'with "thelong sides of 'the 'U paralleljto the long Jside's of :the vrectangular furnace'lbase'and `cooperating with the 'heating meansof the coverto maintainuniform'ity of temperature within the'furnace '2. Inaheati'n'g furnaceh'aving 'a rectangular base and acover, the 'coverbe'ing pro'vided'wi'th lmeans lfor `introducing "heat 'into the "furnace charge and the i base being 'provided With a'plurality"ofsupportsparryinga floor plate on'which 'the furnace 'charge rests, the'improvernent "consisting in that'th'e saidsuppor'ts are free-standing supports spaced 'to 'permit the vfree circulationof'the furnace atmosphereabove 'and below the floor'pla'te, and heating tubes disposed inthe 'center.poition"or1"ly"ofthe base below'the Alicor plate and "between the supports, these heating `tubes cooperating lwith the heating means of i the 'cove'r't'o maitain'uniformity of Atemperature within the furnace.

`3. In'a heating furnace havinga rectangular baseV "and: a' lcover, 4the cover'being provided with means jfor introducing "heat into the furnace burners similar to vthe burner I2 shown in-the parallel leg 9 of the base heating tube.

As I have mentioned, `the heating tubes which I provide lin the furnace base operate in-conjunction with the heating tubes in the furnace cover -to supply heat tozthe charge. Theselbase heating tubes may be controlled independently 'of the others, however, to' achievefadvantageus `results. Thus, when theheating lof a-chargelis commenced, it `maybe-necessary to opera-te-the main heating means at-"lessthan-ful1throttle-to avoid overheating I'the outside regions 'of 4the charge. The Ybase heating meansfhowevennay be operated at full 'heat Voutput tofacilit'ateth'e heating of the oor plate, stool's'and base'"1"ef fractories and thus cut down or even reverse heat transfer from charge :to base. When Athe charge has reached the desiredy temperature and soakcharge and the baisebeing providedwith 'a plurality ofv supports carrying Aa `oor plate on which the Evfurnace'charge rests,'theimprovementconsisting in 'that the' said' vsupports 'are free=stand llng metalsuppots spacedto'permit theI free circlationof the furnace atmosphere'aboveand be- \lo'w"'the"floo`r plate, `yand heating tubes 'disposed in the center portion only of the base below'the floor plateandbe'tweenthe supports, theseheatirig tubesbeingadapted andadjusted to furnish a 'minor portion 'onlyof l'the'heat required 'by the charge and cooperating' with the heating means 'ofi-the' 'cover "toun'ainta'in uniformity of 'temperature Ywithin the furnace. l

'CA'RL"M. YAEGER.

REFERENCES CITED Thesfollowing references iareof .record inthe vfile io'fithis -patent "UNITEDSTATES PATENTS 

